#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main()
{
    int n = 0;
    scanf("%d", &n);
    int sign = 1;
    int result = 0;
    int i = 0;
    for (i = 1; i <= n; i++)
    {
        result += sign * i;
        sign *= (-1);
    }
    printf("%d\n", result);
    return 0;
}